During sleep the human body goes through different phases, and in these phases the body temperature varies both as a result of internal temperature changes in the body during sleep and because of variations of the temperature in the surroundings. These temperature variations disturb the sleep. It is especially important for the sleep that the most important phase—the REM phase—is undisturbed, because in this phase the brain is recharged and prepared for the next waken period. Another effect of the temperature changes is that the quilt covering the person is kicked of during sleep, which often results in the person waking up later on freezing. Further, the temperature changes might also result in sweaty, wet sleeping devices. In both cases the temperature change does not only disturb the sleep, but might also result in sickness.